Diff: mbed-os/rtos/ConditionVariable.h

Revision:

0:9fca2b23d0ba

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mbed-os/rtos/ConditionVariable.h	Sat Feb 23 12:13:36 2019 +0000
@@ -0,0 +1,214 @@
+/* mbed Microcontroller Library
+ * Copyright (c) 2017-2017 ARM Limited
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+#ifndef CONDITIONVARIABLE_H
+#define CONDITIONVARIABLE_H
+
+#include <stdint.h>
+#include "cmsis_os.h"
+#include "rtos/Mutex.h"
+#include "rtos/Semaphore.h"
+
+#include "platform/NonCopyable.h"
+
+namespace rtos {
+/** \addtogroup rtos */
+/** @{*/
+
+struct Waiter;
+
+/** This class provides a safe way to wait for or send notifications of condition changes
+ *
+ * This class is used in conjunction with a mutex to safely wait for or
+ * notify waiters of condition changes to a resource accessible by multiple
+ * threads.
+ *
+ * # Defined behavior
+ * - All threads waiting on the condition variable wake when
+ *   ConditionVariable::notify_all is called.
+ * - If one or more threads are waiting on the condition variable at least
+ *   one of them wakes when ConditionVariable::notify is called.
+ *
+ * # Undefined behavior
+ * - The thread which is unblocked on ConditionVariable::notify_one is
+ *   undefined if there are multiple waiters.
+ * - The order which in which waiting threads acquire the condition variable's
+ *   mutex after ConditionVariable::notify_all is called is undefined.
+ * - When ConditionVariable::notify_one or ConditionVariable::notify_all is
+ *   called and there are one or more waiters and one or more threads attempting
+ *   to acquire the condition variable's mutex the order in which the mutex is
+ *   acquired is undefined.
+ * - The behavior of ConditionVariable::wait and ConditionVariable::wait_for
+ *   is undefined if the condition variable's mutex is locked more than once by
+ *   the calling thread.
+ * - Spurious notifications (not triggered by the application) can occur
+ *   and it is not defined when these occur.
+ *
+ * @note Synchronization level: Thread safe
+ *
+ * Example:
+ * @code
+ * #include "mbed.h"
+ *
+ * Mutex mutex;
+ * ConditionVariable cond(mutex);
+ *
+ * // These variables are protected by locking mutex
+ * uint32_t count = 0;
+ * bool done = false;
+ *
+ * void worker_thread()
+ * {
+ *     mutex.lock();
+ *     do {
+ *         printf("Worker: Count %lu\r\n", count);
+ *
+ *         // Wait for a condition to change
+ *         cond.wait();
+ *
+ *     } while (!done);
+ *     printf("Worker: Exiting\r\n");
+ *     mutex.unlock();
+ * }
+ *
+ * int main() {
+ *     Thread thread;
+ *     thread.start(worker_thread);
+ *
+ *     for (int i = 0; i < 5; i++) {
+ *
+ *         mutex.lock();
+ *         // Change count and notify waiters of this
+ *         count++;
+ *         printf("Main: Set count to %lu\r\n", count);
+ *         cond.notify_all();
+ *         mutex.unlock();
+ *
+ *         wait(1.0);
+ *     }
+ *
+ *     mutex.lock();
+ *     // Change done and notify waiters of this
+ *     done = true;
+ *     printf("Main: Set done\r\n");
+ *     cond.notify_all();
+ *     mutex.unlock();
+ *
+ *     thread.join();
+ * }
+ * @endcode
+ */
+class ConditionVariable : private mbed::NonCopyable<ConditionVariable> {
+public:
+    /** Create and Initialize a ConditionVariable object */
+    ConditionVariable(Mutex &mutex);
+
+    /** Wait for a notification
+     *
+     * Wait until a notification occurs.
+     *
+     * @note - The thread calling this function must be the owner of the
+     * ConditionVariable's mutex and it must be locked exactly once
+     * @note - Spurious notifications can occur so the caller of this API
+     * should check to make sure the condition they are waiting on has
+     * been met
+     *
+     * Example:
+     * @code
+     * mutex.lock();
+     * while (!condition_met) {
+     *     cond.wait();
+     * }
+     *
+     * function_to_handle_condition();
+     *
+     * mutex.unlock();
+     * @endcode
+     */
+    void wait();
+
+    /** Wait for a notification or timeout
+     *
+     * @param   millisec  timeout value or osWaitForever in case of no time-out.
+     * @return  true if a timeout occurred, false otherwise.
+     *
+     * @note - The thread calling this function must be the owner of the
+     * ConditionVariable's mutex and it must be locked exactly once
+     * @note - Spurious notifications can occur so the caller of this API
+     * should check to make sure the condition they are waiting on has
+     * been met
+     *
+     * Example:
+     * @code
+     * mutex.lock();
+     * Timer timer;
+     * timer.start();
+     *
+     * bool timed_out = false;
+     * uint32_t time_left = TIMEOUT;
+     * while (!condition_met && !timed_out) {
+     *     timed_out = cond.wait_for(time_left);
+     *     uint32_t elapsed = timer.read_ms();
+     *     time_left = elapsed > TIMEOUT ? 0 : TIMEOUT - elapsed;
+     * }
+     *
+     * if (condition_met) {
+     *     function_to_handle_condition();
+     * }
+     *
+     * mutex.unlock();
+     * @endcode
+     */
+    bool wait_for(uint32_t millisec);
+
+    /** Notify one waiter on this condition variable that a condition changed.
+     *
+     * @note - The thread calling this function must be the owner of the ConditionVariable's mutex
+     */
+    void notify_one();
+
+    /** Notify all waiters on this condition variable that a condition changed.
+     *
+     * @note - The thread calling this function must be the owner of the ConditionVariable's mutex
+     */
+    void notify_all();
+
+    ~ConditionVariable();
+
+protected:
+    struct Waiter {
+        Waiter();
+        Semaphore sem;
+        Waiter *prev;
+        Waiter *next;
+        bool in_list;
+    };
+
+    static void _add_wait_list(Waiter **wait_list, Waiter *waiter);
+    static void _remove_wait_list(Waiter **wait_list, Waiter *waiter);
+    Mutex &_mutex;
+    Waiter *_wait_list;
+};
+
+}
+#endif
+
+/** @}*/